1. Field of the Invention
The present invention relates generally to a plasma etching apparatus and, more particularly, to a plasma etching apparatus employed in a semiconductor device manufacturing system.
2. Description of the Related Art
A magnetron plasma etching apparatus is employed in a semiconductor device manufacturing system. In the magnetron plasma etching apparatus, a magnetic field is generated so as to intersect an electric field at right angles which is generated between parallel electrodes, thereby attaining a higher etching rate (about 1 .mu./min) at a lower pressure (about 10.sup.-3 torr). In addition, in the magnetron plasma etching apparatus, a magnet serving as means for generating a magnetic field is rotated, thereby making the magnetic field uniform and enhancing etching characteristics.
In this type of apparatus, it is an indispensable condition to exactly detect an etching end-point, for the subsequent processing. For this purpose, a transparent window is formed in a plasma-producing process chamber, and an etching end-point detector (EPD) is situated so as to face the window. The EPD detects the intensity of all light emitted from the intra-chamber atmosphere by a plasma ("intra-chamber emission light), and, as shown in, for example, FIG. 6, an etching end-point is determined when the emission light intensity has decreased to 60% (100% in the normal etching state).
In this etching end-point detector, however, the etching end-point is detected on the basis of the degree of variance in intra-chamber emission light intensity, as has been stated above. Thus, when a wafer of a low aperture rate, which has a narrow etching area, is treated, it is difficult to exactly detect the etching end-point. That is, when the aperture rate in etching is low, the degree of variance in intra-chamber emission light intensity is low. The aperture rate decreases in accordance with the advancement of semiconductor device integration.
Further, when the magnet is rotated to rotate the magnetic field, as stated above, the region of a high plasma density moves and consequently the intra-chamber emission light intensity detected by the EPD varies. It is therefore more difficult to detect the variance in intra-chamber emission light intensity in the case of carrying out the low-aperture-rate etching. It is substantially impossible to detect the etching end-point.
This drawback is conspicuous when the aperture rate of a wafer is 5% or less. In these years, a still lower aperture rate is required in accordance with higher integration of semiconductor devices. For example, in the manufacture of a 16 M-Byte semiconductor memory, it is required that the etching end-point be exactly detected under a condition of 3% or lower aperture rate.